This article breaks down the key injection molding parameters for common plastics, offering real-world data and shop-floor insights to help mold engineers optimize cycle times and part quality.

Getting process parameters right is half the battle in injection molding. For amorphous materials like ABS and PC, melt temperature is the first thing I check. ABS typically runs at 210–250°C, with mold temperature between 40–80°C. If you push ABS above 260°C, you risk degradation and visible streaking on the part surface. For PC, the window is tighter: 280–320°C melt, and a mold surface of 80–120°C is non-negotiable if you want to avoid internal stress cracks. Injection pressure for these materials usually lands between 80–140 MPa, but the real trick is holding pressure—set it at 50–70% of injection pressure to minimize sink marks without overpacking the cavity.

Semi-crystalline resins like PA66 and POM behave differently. PA66 demands a melt temperature of 260–290°C, and mold temperature should be 60–90°C for standard grades, but if you're chasing high dimensional stability, go to 100–120°C. The shrinkage rate for PA66 is around 1.5–2.0%, so your core and cavity dimensions must account for that upfront. POM is more forgiving on melt (190–220°C) but hates shear heat—use a slower injection speed and keep back pressure below 0.5 MPa to avoid gassing and surface delamination. For both, cooling time is often underestimated; a 2 mm wall thickness at 80°C mold temperature needs at least 20–25 seconds of cooling to reach safe ejection stiffness.

One thing many young engineers overlook is the interaction between wall thickness and packing profile. For a 3 mm ABS part, I typically use a two-stage hold: high pressure for 2 seconds to seal the gate, then drop to 40% for 4 seconds to compensate for volumetric shrinkage. This cuts cycle time by 8–12% compared to a constant hold. Also, always verify your actual melt temperature with a hand pyrometer on the nozzle—barrel readings can be off by 15–20°C. If you're struggling with warpage on glass-filled materials, raise mold temperature by 10°C and reduce injection speed by 15%; that alone fixes most flatness issues. For deeper troubleshooting, visiting MoldWorld at www.moldw.com gives you access to a solid library of mold design and process optimization case studies, straight from working tool shops.